The present invention relates to a preparing method of 2-phenylalkanoic acid derivatives and more particularly, to the preparing method of 2-phenylalkanoic acid derivatives expressed by formula 1 from 5,6-dlihydro-2(4H)-benzofuranoneas a starting material in the presence of a catalyst, organic acid alkali metal salt, in a mild condition, 
wherein R1 represents benzoyl, naphthoyl, nicotinoyl, furoyl or thenoyl group; and R2 represents a hydrogen atom or C1xcx9cC6 alkyl group.
2-Phenylalkanoic acid derivatives expressed by formula 1 is widely known and used as pharmaceutical drugs as well as a major intermediate for the synthesis of various pharmaceutical drugs [Brit. Med. J. 1992, 4, 398].
Also, the preparing methods of 2-Phenylalkanoic acid derivatives expressed by formula 1 have being developed extensively and some representative examples are disclosed in DE 2,624,174, Tetralzedron Lett. 1979, 46, 4499 and Syntlwesis, 1979, 434. In conventional preparing methods, the reactions are performed in the presence of excess pyridinium hydrogen chloride salt as in the following scheme 1, 
wherein R1 and R2 are the same as explained above.
However, the above conventional preparing methods are undesirable in requirement of extra controlling system for corrosion in chemical plants due to use of excess amount of pyridinium hydrochloric acid salt (about 11 equivalents excess) possessing strong corrosion with heating at 230xc2x0 C. On top of that, these methods are economnically unfavorable for excess use of expensive pyridinium hydrochloric acid salt and industrially unfavorable for requirement of special carefulness to carry pyridinium hydrochloric acid salt due to its powerful hygroscopicity. When pyridinium hydrochloric acid salt is used less than 1 equivalent, the reactivity is too low to use for industrial purpose. Using of pyridinium hydrochloric acid salt can be also dangerous by blocking a condenser when it gets cool down by turning to solid due to its sublimation property at high temperature.
The inventors made extensive efforts to solve the problems of the conventional preparing methods. As a result, it was realized that the use of organic acid alkali metal salt instead of expensive pyridinium hydrocliloric acid salt as a reaction catalyst could solve all the said problems.
Thus, an object of the present invention is to provide an industrially advantageous preparing method of 2-phenylalkanoic acid derivatives from 5,6-dihydro-2(4H)-benzofuranone in the presence of alkali catalyst, organic acid alkali metal salt.